1 //===--- CGVTables.cpp - Emit LLVM Code for C++ vtables -------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This contains code dealing with C++ code generation of virtual tables.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "CodeGenFunction.h"
15 #include "CGCXXABI.h"
16 #include "CodeGenModule.h"
17 #include "clang/AST/CXXInheritance.h"
18 #include "clang/AST/RecordLayout.h"
19 #include "clang/CodeGen/CGFunctionInfo.h"
20 #include "clang/Frontend/CodeGenOptions.h"
21 #include "llvm/ADT/DenseSet.h"
22 #include "llvm/ADT/SetVector.h"
23 #include "llvm/Support/Compiler.h"
24 #include "llvm/Support/Format.h"
25 #include "llvm/Transforms/Utils/Cloning.h"
26 #include <algorithm>
27 #include <cstdio>
28
29 using namespace clang;
30 using namespace CodeGen;
31
CodeGenVTables(CodeGenModule & CGM)32 CodeGenVTables::CodeGenVTables(CodeGenModule &CGM)
33 : CGM(CGM), VTContext(CGM.getContext().getVTableContext()) {}
34
GetAddrOfThunk(GlobalDecl GD,const ThunkInfo & Thunk)35 llvm::Constant *CodeGenModule::GetAddrOfThunk(GlobalDecl GD,
36 const ThunkInfo &Thunk) {
37 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
38
39 // Compute the mangled name.
40 SmallString<256> Name;
41 llvm::raw_svector_ostream Out(Name);
42 if (const CXXDestructorDecl* DD = dyn_cast<CXXDestructorDecl>(MD))
43 getCXXABI().getMangleContext().mangleCXXDtorThunk(DD, GD.getDtorType(),
44 Thunk.This, Out);
45 else
46 getCXXABI().getMangleContext().mangleThunk(MD, Thunk, Out);
47 Out.flush();
48
49 llvm::Type *Ty = getTypes().GetFunctionTypeForVTable(GD);
50 return GetOrCreateLLVMFunction(Name, Ty, GD, /*ForVTable=*/true,
51 /*DontDefer=*/true, /*IsThunk=*/true);
52 }
53
setThunkVisibility(CodeGenModule & CGM,const CXXMethodDecl * MD,const ThunkInfo & Thunk,llvm::Function * Fn)54 static void setThunkVisibility(CodeGenModule &CGM, const CXXMethodDecl *MD,
55 const ThunkInfo &Thunk, llvm::Function *Fn) {
56 CGM.setGlobalVisibility(Fn, MD);
57 }
58
59 #ifndef NDEBUG
similar(const ABIArgInfo & infoL,CanQualType typeL,const ABIArgInfo & infoR,CanQualType typeR)60 static bool similar(const ABIArgInfo &infoL, CanQualType typeL,
61 const ABIArgInfo &infoR, CanQualType typeR) {
62 return (infoL.getKind() == infoR.getKind() &&
63 (typeL == typeR ||
64 (isa<PointerType>(typeL) && isa<PointerType>(typeR)) ||
65 (isa<ReferenceType>(typeL) && isa<ReferenceType>(typeR))));
66 }
67 #endif
68
PerformReturnAdjustment(CodeGenFunction & CGF,QualType ResultType,RValue RV,const ThunkInfo & Thunk)69 static RValue PerformReturnAdjustment(CodeGenFunction &CGF,
70 QualType ResultType, RValue RV,
71 const ThunkInfo &Thunk) {
72 // Emit the return adjustment.
73 bool NullCheckValue = !ResultType->isReferenceType();
74
75 llvm::BasicBlock *AdjustNull = nullptr;
76 llvm::BasicBlock *AdjustNotNull = nullptr;
77 llvm::BasicBlock *AdjustEnd = nullptr;
78
79 llvm::Value *ReturnValue = RV.getScalarVal();
80
81 if (NullCheckValue) {
82 AdjustNull = CGF.createBasicBlock("adjust.null");
83 AdjustNotNull = CGF.createBasicBlock("adjust.notnull");
84 AdjustEnd = CGF.createBasicBlock("adjust.end");
85
86 llvm::Value *IsNull = CGF.Builder.CreateIsNull(ReturnValue);
87 CGF.Builder.CreateCondBr(IsNull, AdjustNull, AdjustNotNull);
88 CGF.EmitBlock(AdjustNotNull);
89 }
90
91 ReturnValue = CGF.CGM.getCXXABI().performReturnAdjustment(CGF, ReturnValue,
92 Thunk.Return);
93
94 if (NullCheckValue) {
95 CGF.Builder.CreateBr(AdjustEnd);
96 CGF.EmitBlock(AdjustNull);
97 CGF.Builder.CreateBr(AdjustEnd);
98 CGF.EmitBlock(AdjustEnd);
99
100 llvm::PHINode *PHI = CGF.Builder.CreatePHI(ReturnValue->getType(), 2);
101 PHI->addIncoming(ReturnValue, AdjustNotNull);
102 PHI->addIncoming(llvm::Constant::getNullValue(ReturnValue->getType()),
103 AdjustNull);
104 ReturnValue = PHI;
105 }
106
107 return RValue::get(ReturnValue);
108 }
109
110 // This function does roughly the same thing as GenerateThunk, but in a
111 // very different way, so that va_start and va_end work correctly.
112 // FIXME: This function assumes "this" is the first non-sret LLVM argument of
113 // a function, and that there is an alloca built in the entry block
114 // for all accesses to "this".
115 // FIXME: This function assumes there is only one "ret" statement per function.
116 // FIXME: Cloning isn't correct in the presence of indirect goto!
117 // FIXME: This implementation of thunks bloats codesize by duplicating the
118 // function definition. There are alternatives:
119 // 1. Add some sort of stub support to LLVM for cases where we can
120 // do a this adjustment, then a sibcall.
121 // 2. We could transform the definition to take a va_list instead of an
122 // actual variable argument list, then have the thunks (including a
123 // no-op thunk for the regular definition) call va_start/va_end.
124 // There's a bit of per-call overhead for this solution, but it's
125 // better for codesize if the definition is long.
GenerateVarArgsThunk(llvm::Function * Fn,const CGFunctionInfo & FnInfo,GlobalDecl GD,const ThunkInfo & Thunk)126 void CodeGenFunction::GenerateVarArgsThunk(
127 llvm::Function *Fn,
128 const CGFunctionInfo &FnInfo,
129 GlobalDecl GD, const ThunkInfo &Thunk) {
130 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
131 const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
132 QualType ResultType = FPT->getReturnType();
133
134 // Get the original function
135 assert(FnInfo.isVariadic());
136 llvm::Type *Ty = CGM.getTypes().GetFunctionType(FnInfo);
137 llvm::Value *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
138 llvm::Function *BaseFn = cast<llvm::Function>(Callee);
139
140 // Clone to thunk.
141 llvm::ValueToValueMapTy VMap;
142 llvm::Function *NewFn = llvm::CloneFunction(BaseFn, VMap,
143 /*ModuleLevelChanges=*/false);
144 CGM.getModule().getFunctionList().push_back(NewFn);
145 Fn->replaceAllUsesWith(NewFn);
146 NewFn->takeName(Fn);
147 Fn->eraseFromParent();
148 Fn = NewFn;
149
150 // "Initialize" CGF (minimally).
151 CurFn = Fn;
152
153 // Get the "this" value
154 llvm::Function::arg_iterator AI = Fn->arg_begin();
155 if (CGM.ReturnTypeUsesSRet(FnInfo))
156 ++AI;
157
158 // Find the first store of "this", which will be to the alloca associated
159 // with "this".
160 llvm::Value *ThisPtr = &*AI;
161 llvm::BasicBlock *EntryBB = Fn->begin();
162 llvm::Instruction *ThisStore =
163 std::find_if(EntryBB->begin(), EntryBB->end(), [&](llvm::Instruction &I) {
164 return isa<llvm::StoreInst>(I) && I.getOperand(0) == ThisPtr;
165 });
166 assert(ThisStore && "Store of this should be in entry block?");
167 // Adjust "this", if necessary.
168 Builder.SetInsertPoint(ThisStore);
169 llvm::Value *AdjustedThisPtr =
170 CGM.getCXXABI().performThisAdjustment(*this, ThisPtr, Thunk.This);
171 ThisStore->setOperand(0, AdjustedThisPtr);
172
173 if (!Thunk.Return.isEmpty()) {
174 // Fix up the returned value, if necessary.
175 for (llvm::Function::iterator I = Fn->begin(), E = Fn->end(); I != E; I++) {
176 llvm::Instruction *T = I->getTerminator();
177 if (isa<llvm::ReturnInst>(T)) {
178 RValue RV = RValue::get(T->getOperand(0));
179 T->eraseFromParent();
180 Builder.SetInsertPoint(&*I);
181 RV = PerformReturnAdjustment(*this, ResultType, RV, Thunk);
182 Builder.CreateRet(RV.getScalarVal());
183 break;
184 }
185 }
186 }
187 }
188
StartThunk(llvm::Function * Fn,GlobalDecl GD,const CGFunctionInfo & FnInfo)189 void CodeGenFunction::StartThunk(llvm::Function *Fn, GlobalDecl GD,
190 const CGFunctionInfo &FnInfo) {
191 assert(!CurGD.getDecl() && "CurGD was already set!");
192 CurGD = GD;
193 CurFuncIsThunk = true;
194
195 // Build FunctionArgs.
196 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
197 QualType ThisType = MD->getThisType(getContext());
198 const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
199 QualType ResultType = CGM.getCXXABI().HasThisReturn(GD)
200 ? ThisType
201 : CGM.getCXXABI().hasMostDerivedReturn(GD)
202 ? CGM.getContext().VoidPtrTy
203 : FPT->getReturnType();
204 FunctionArgList FunctionArgs;
205
206 // Create the implicit 'this' parameter declaration.
207 CGM.getCXXABI().buildThisParam(*this, FunctionArgs);
208
209 // Add the rest of the parameters.
210 FunctionArgs.append(MD->param_begin(), MD->param_end());
211
212 if (isa<CXXDestructorDecl>(MD))
213 CGM.getCXXABI().addImplicitStructorParams(*this, ResultType, FunctionArgs);
214
215 // Start defining the function.
216 StartFunction(GlobalDecl(), ResultType, Fn, FnInfo, FunctionArgs,
217 MD->getLocation(), MD->getLocation());
218
219 // Since we didn't pass a GlobalDecl to StartFunction, do this ourselves.
220 CGM.getCXXABI().EmitInstanceFunctionProlog(*this);
221 CXXThisValue = CXXABIThisValue;
222 }
223
EmitCallAndReturnForThunk(llvm::Value * Callee,const ThunkInfo * Thunk)224 void CodeGenFunction::EmitCallAndReturnForThunk(llvm::Value *Callee,
225 const ThunkInfo *Thunk) {
226 assert(isa<CXXMethodDecl>(CurGD.getDecl()) &&
227 "Please use a new CGF for this thunk");
228 const CXXMethodDecl *MD = cast<CXXMethodDecl>(CurGD.getDecl());
229
230 // Adjust the 'this' pointer if necessary
231 llvm::Value *AdjustedThisPtr = Thunk ? CGM.getCXXABI().performThisAdjustment(
232 *this, LoadCXXThis(), Thunk->This)
233 : LoadCXXThis();
234
235 if (CurFnInfo->usesInAlloca()) {
236 // We don't handle return adjusting thunks, because they require us to call
237 // the copy constructor. For now, fall through and pretend the return
238 // adjustment was empty so we don't crash.
239 if (Thunk && !Thunk->Return.isEmpty()) {
240 CGM.ErrorUnsupported(
241 MD, "non-trivial argument copy for return-adjusting thunk");
242 }
243 EmitMustTailThunk(MD, AdjustedThisPtr, Callee);
244 return;
245 }
246
247 // Start building CallArgs.
248 CallArgList CallArgs;
249 QualType ThisType = MD->getThisType(getContext());
250 CallArgs.add(RValue::get(AdjustedThisPtr), ThisType);
251
252 if (isa<CXXDestructorDecl>(MD))
253 CGM.getCXXABI().adjustCallArgsForDestructorThunk(*this, CurGD, CallArgs);
254
255 // Add the rest of the arguments.
256 for (const ParmVarDecl *PD : MD->params())
257 EmitDelegateCallArg(CallArgs, PD, PD->getLocStart());
258
259 const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
260
261 #ifndef NDEBUG
262 const CGFunctionInfo &CallFnInfo =
263 CGM.getTypes().arrangeCXXMethodCall(CallArgs, FPT,
264 RequiredArgs::forPrototypePlus(FPT, 1));
265 assert(CallFnInfo.getRegParm() == CurFnInfo->getRegParm() &&
266 CallFnInfo.isNoReturn() == CurFnInfo->isNoReturn() &&
267 CallFnInfo.getCallingConvention() == CurFnInfo->getCallingConvention());
268 assert(isa<CXXDestructorDecl>(MD) || // ignore dtor return types
269 similar(CallFnInfo.getReturnInfo(), CallFnInfo.getReturnType(),
270 CurFnInfo->getReturnInfo(), CurFnInfo->getReturnType()));
271 assert(CallFnInfo.arg_size() == CurFnInfo->arg_size());
272 for (unsigned i = 0, e = CurFnInfo->arg_size(); i != e; ++i)
273 assert(similar(CallFnInfo.arg_begin()[i].info,
274 CallFnInfo.arg_begin()[i].type,
275 CurFnInfo->arg_begin()[i].info,
276 CurFnInfo->arg_begin()[i].type));
277 #endif
278
279 // Determine whether we have a return value slot to use.
280 QualType ResultType = CGM.getCXXABI().HasThisReturn(CurGD)
281 ? ThisType
282 : CGM.getCXXABI().hasMostDerivedReturn(CurGD)
283 ? CGM.getContext().VoidPtrTy
284 : FPT->getReturnType();
285 ReturnValueSlot Slot;
286 if (!ResultType->isVoidType() &&
287 CurFnInfo->getReturnInfo().getKind() == ABIArgInfo::Indirect &&
288 !hasScalarEvaluationKind(CurFnInfo->getReturnType()))
289 Slot = ReturnValueSlot(ReturnValue, ResultType.isVolatileQualified());
290
291 // Now emit our call.
292 llvm::Instruction *CallOrInvoke;
293 RValue RV = EmitCall(*CurFnInfo, Callee, Slot, CallArgs, MD, &CallOrInvoke);
294
295 // Consider return adjustment if we have ThunkInfo.
296 if (Thunk && !Thunk->Return.isEmpty())
297 RV = PerformReturnAdjustment(*this, ResultType, RV, *Thunk);
298
299 // Emit return.
300 if (!ResultType->isVoidType() && Slot.isNull())
301 CGM.getCXXABI().EmitReturnFromThunk(*this, RV, ResultType);
302
303 // Disable the final ARC autorelease.
304 AutoreleaseResult = false;
305
306 FinishFunction();
307 }
308
EmitMustTailThunk(const CXXMethodDecl * MD,llvm::Value * AdjustedThisPtr,llvm::Value * Callee)309 void CodeGenFunction::EmitMustTailThunk(const CXXMethodDecl *MD,
310 llvm::Value *AdjustedThisPtr,
311 llvm::Value *Callee) {
312 // Emitting a musttail call thunk doesn't use any of the CGCall.cpp machinery
313 // to translate AST arguments into LLVM IR arguments. For thunks, we know
314 // that the caller prototype more or less matches the callee prototype with
315 // the exception of 'this'.
316 SmallVector<llvm::Value *, 8> Args;
317 for (llvm::Argument &A : CurFn->args())
318 Args.push_back(&A);
319
320 // Set the adjusted 'this' pointer.
321 const ABIArgInfo &ThisAI = CurFnInfo->arg_begin()->info;
322 if (ThisAI.isDirect()) {
323 const ABIArgInfo &RetAI = CurFnInfo->getReturnInfo();
324 int ThisArgNo = RetAI.isIndirect() && !RetAI.isSRetAfterThis() ? 1 : 0;
325 llvm::Type *ThisType = Args[ThisArgNo]->getType();
326 if (ThisType != AdjustedThisPtr->getType())
327 AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);
328 Args[ThisArgNo] = AdjustedThisPtr;
329 } else {
330 assert(ThisAI.isInAlloca() && "this is passed directly or inalloca");
331 llvm::Value *ThisAddr = GetAddrOfLocalVar(CXXABIThisDecl);
332 llvm::Type *ThisType =
333 cast<llvm::PointerType>(ThisAddr->getType())->getElementType();
334 if (ThisType != AdjustedThisPtr->getType())
335 AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);
336 Builder.CreateStore(AdjustedThisPtr, ThisAddr);
337 }
338
339 // Emit the musttail call manually. Even if the prologue pushed cleanups, we
340 // don't actually want to run them.
341 llvm::CallInst *Call = Builder.CreateCall(Callee, Args);
342 Call->setTailCallKind(llvm::CallInst::TCK_MustTail);
343
344 // Apply the standard set of call attributes.
345 unsigned CallingConv;
346 CodeGen::AttributeListType AttributeList;
347 CGM.ConstructAttributeList(*CurFnInfo, MD, AttributeList, CallingConv,
348 /*AttrOnCallSite=*/true);
349 llvm::AttributeSet Attrs =
350 llvm::AttributeSet::get(getLLVMContext(), AttributeList);
351 Call->setAttributes(Attrs);
352 Call->setCallingConv(static_cast<llvm::CallingConv::ID>(CallingConv));
353
354 if (Call->getType()->isVoidTy())
355 Builder.CreateRetVoid();
356 else
357 Builder.CreateRet(Call);
358
359 // Finish the function to maintain CodeGenFunction invariants.
360 // FIXME: Don't emit unreachable code.
361 EmitBlock(createBasicBlock());
362 FinishFunction();
363 }
364
GenerateThunk(llvm::Function * Fn,const CGFunctionInfo & FnInfo,GlobalDecl GD,const ThunkInfo & Thunk)365 void CodeGenFunction::GenerateThunk(llvm::Function *Fn,
366 const CGFunctionInfo &FnInfo,
367 GlobalDecl GD, const ThunkInfo &Thunk) {
368 StartThunk(Fn, GD, FnInfo);
369
370 // Get our callee.
371 llvm::Type *Ty =
372 CGM.getTypes().GetFunctionType(CGM.getTypes().arrangeGlobalDeclaration(GD));
373 llvm::Value *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
374
375 // Make the call and return the result.
376 EmitCallAndReturnForThunk(Callee, &Thunk);
377
378 // Set the right linkage.
379 CGM.setFunctionLinkage(GD, Fn);
380
381 // Set the right visibility.
382 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
383 setThunkVisibility(CGM, MD, Thunk, Fn);
384 }
385
emitThunk(GlobalDecl GD,const ThunkInfo & Thunk,bool ForVTable)386 void CodeGenVTables::emitThunk(GlobalDecl GD, const ThunkInfo &Thunk,
387 bool ForVTable) {
388 const CGFunctionInfo &FnInfo = CGM.getTypes().arrangeGlobalDeclaration(GD);
389
390 // FIXME: re-use FnInfo in this computation.
391 llvm::Constant *C = CGM.GetAddrOfThunk(GD, Thunk);
392 llvm::GlobalValue *Entry;
393
394 // Strip off a bitcast if we got one back.
395 if (llvm::ConstantExpr *CE = dyn_cast<llvm::ConstantExpr>(C)) {
396 assert(CE->getOpcode() == llvm::Instruction::BitCast);
397 Entry = cast<llvm::GlobalValue>(CE->getOperand(0));
398 } else {
399 Entry = cast<llvm::GlobalValue>(C);
400 }
401
402 // There's already a declaration with the same name, check if it has the same
403 // type or if we need to replace it.
404 if (Entry->getType()->getElementType() !=
405 CGM.getTypes().GetFunctionTypeForVTable(GD)) {
406 llvm::GlobalValue *OldThunkFn = Entry;
407
408 // If the types mismatch then we have to rewrite the definition.
409 assert(OldThunkFn->isDeclaration() &&
410 "Shouldn't replace non-declaration");
411
412 // Remove the name from the old thunk function and get a new thunk.
413 OldThunkFn->setName(StringRef());
414 Entry = cast<llvm::GlobalValue>(CGM.GetAddrOfThunk(GD, Thunk));
415
416 // If needed, replace the old thunk with a bitcast.
417 if (!OldThunkFn->use_empty()) {
418 llvm::Constant *NewPtrForOldDecl =
419 llvm::ConstantExpr::getBitCast(Entry, OldThunkFn->getType());
420 OldThunkFn->replaceAllUsesWith(NewPtrForOldDecl);
421 }
422
423 // Remove the old thunk.
424 OldThunkFn->eraseFromParent();
425 }
426
427 llvm::Function *ThunkFn = cast<llvm::Function>(Entry);
428 bool ABIHasKeyFunctions = CGM.getTarget().getCXXABI().hasKeyFunctions();
429 bool UseAvailableExternallyLinkage = ForVTable && ABIHasKeyFunctions;
430
431 if (!ThunkFn->isDeclaration()) {
432 if (!ABIHasKeyFunctions || UseAvailableExternallyLinkage) {
433 // There is already a thunk emitted for this function, do nothing.
434 return;
435 }
436
437 // Change the linkage.
438 CGM.setFunctionLinkage(GD, ThunkFn);
439 return;
440 }
441
442 CGM.SetLLVMFunctionAttributesForDefinition(GD.getDecl(), ThunkFn);
443
444 if (ThunkFn->isVarArg()) {
445 // Varargs thunks are special; we can't just generate a call because
446 // we can't copy the varargs. Our implementation is rather
447 // expensive/sucky at the moment, so don't generate the thunk unless
448 // we have to.
449 // FIXME: Do something better here; GenerateVarArgsThunk is extremely ugly.
450 if (!UseAvailableExternallyLinkage) {
451 CodeGenFunction(CGM).GenerateVarArgsThunk(ThunkFn, FnInfo, GD, Thunk);
452 CGM.getCXXABI().setThunkLinkage(ThunkFn, ForVTable, GD,
453 !Thunk.Return.isEmpty());
454 }
455 } else {
456 // Normal thunk body generation.
457 CodeGenFunction(CGM).GenerateThunk(ThunkFn, FnInfo, GD, Thunk);
458 CGM.getCXXABI().setThunkLinkage(ThunkFn, ForVTable, GD,
459 !Thunk.Return.isEmpty());
460 }
461 }
462
maybeEmitThunkForVTable(GlobalDecl GD,const ThunkInfo & Thunk)463 void CodeGenVTables::maybeEmitThunkForVTable(GlobalDecl GD,
464 const ThunkInfo &Thunk) {
465 // If the ABI has key functions, only the TU with the key function should emit
466 // the thunk. However, we can allow inlining of thunks if we emit them with
467 // available_externally linkage together with vtables when optimizations are
468 // enabled.
469 if (CGM.getTarget().getCXXABI().hasKeyFunctions() &&
470 !CGM.getCodeGenOpts().OptimizationLevel)
471 return;
472
473 // We can't emit thunks for member functions with incomplete types.
474 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
475 if (!CGM.getTypes().isFuncTypeConvertible(
476 MD->getType()->castAs<FunctionType>()))
477 return;
478
479 emitThunk(GD, Thunk, /*ForVTable=*/true);
480 }
481
EmitThunks(GlobalDecl GD)482 void CodeGenVTables::EmitThunks(GlobalDecl GD)
483 {
484 const CXXMethodDecl *MD =
485 cast<CXXMethodDecl>(GD.getDecl())->getCanonicalDecl();
486
487 // We don't need to generate thunks for the base destructor.
488 if (isa<CXXDestructorDecl>(MD) && GD.getDtorType() == Dtor_Base)
489 return;
490
491 const VTableContextBase::ThunkInfoVectorTy *ThunkInfoVector =
492 VTContext->getThunkInfo(GD);
493
494 if (!ThunkInfoVector)
495 return;
496
497 for (unsigned I = 0, E = ThunkInfoVector->size(); I != E; ++I)
498 emitThunk(GD, (*ThunkInfoVector)[I], /*ForVTable=*/false);
499 }
500
CreateVTableInitializer(const CXXRecordDecl * RD,const VTableComponent * Components,unsigned NumComponents,const VTableLayout::VTableThunkTy * VTableThunks,unsigned NumVTableThunks,llvm::Constant * RTTI)501 llvm::Constant *CodeGenVTables::CreateVTableInitializer(
502 const CXXRecordDecl *RD, const VTableComponent *Components,
503 unsigned NumComponents, const VTableLayout::VTableThunkTy *VTableThunks,
504 unsigned NumVTableThunks, llvm::Constant *RTTI) {
505 SmallVector<llvm::Constant *, 64> Inits;
506
507 llvm::Type *Int8PtrTy = CGM.Int8PtrTy;
508
509 llvm::Type *PtrDiffTy =
510 CGM.getTypes().ConvertType(CGM.getContext().getPointerDiffType());
511
512 unsigned NextVTableThunkIndex = 0;
513
514 llvm::Constant *PureVirtualFn = nullptr, *DeletedVirtualFn = nullptr;
515
516 for (unsigned I = 0; I != NumComponents; ++I) {
517 VTableComponent Component = Components[I];
518
519 llvm::Constant *Init = nullptr;
520
521 switch (Component.getKind()) {
522 case VTableComponent::CK_VCallOffset:
523 Init = llvm::ConstantInt::get(PtrDiffTy,
524 Component.getVCallOffset().getQuantity());
525 Init = llvm::ConstantExpr::getIntToPtr(Init, Int8PtrTy);
526 break;
527 case VTableComponent::CK_VBaseOffset:
528 Init = llvm::ConstantInt::get(PtrDiffTy,
529 Component.getVBaseOffset().getQuantity());
530 Init = llvm::ConstantExpr::getIntToPtr(Init, Int8PtrTy);
531 break;
532 case VTableComponent::CK_OffsetToTop:
533 Init = llvm::ConstantInt::get(PtrDiffTy,
534 Component.getOffsetToTop().getQuantity());
535 Init = llvm::ConstantExpr::getIntToPtr(Init, Int8PtrTy);
536 break;
537 case VTableComponent::CK_RTTI:
538 Init = llvm::ConstantExpr::getBitCast(RTTI, Int8PtrTy);
539 break;
540 case VTableComponent::CK_FunctionPointer:
541 case VTableComponent::CK_CompleteDtorPointer:
542 case VTableComponent::CK_DeletingDtorPointer: {
543 GlobalDecl GD;
544
545 // Get the right global decl.
546 switch (Component.getKind()) {
547 default:
548 llvm_unreachable("Unexpected vtable component kind");
549 case VTableComponent::CK_FunctionPointer:
550 GD = Component.getFunctionDecl();
551 break;
552 case VTableComponent::CK_CompleteDtorPointer:
553 GD = GlobalDecl(Component.getDestructorDecl(), Dtor_Complete);
554 break;
555 case VTableComponent::CK_DeletingDtorPointer:
556 GD = GlobalDecl(Component.getDestructorDecl(), Dtor_Deleting);
557 break;
558 }
559
560 if (cast<CXXMethodDecl>(GD.getDecl())->isPure()) {
561 // We have a pure virtual member function.
562 if (!PureVirtualFn) {
563 llvm::FunctionType *Ty =
564 llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
565 StringRef PureCallName = CGM.getCXXABI().GetPureVirtualCallName();
566 PureVirtualFn = CGM.CreateRuntimeFunction(Ty, PureCallName);
567 PureVirtualFn = llvm::ConstantExpr::getBitCast(PureVirtualFn,
568 CGM.Int8PtrTy);
569 }
570 Init = PureVirtualFn;
571 } else if (cast<CXXMethodDecl>(GD.getDecl())->isDeleted()) {
572 if (!DeletedVirtualFn) {
573 llvm::FunctionType *Ty =
574 llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
575 StringRef DeletedCallName =
576 CGM.getCXXABI().GetDeletedVirtualCallName();
577 DeletedVirtualFn = CGM.CreateRuntimeFunction(Ty, DeletedCallName);
578 DeletedVirtualFn = llvm::ConstantExpr::getBitCast(DeletedVirtualFn,
579 CGM.Int8PtrTy);
580 }
581 Init = DeletedVirtualFn;
582 } else {
583 // Check if we should use a thunk.
584 if (NextVTableThunkIndex < NumVTableThunks &&
585 VTableThunks[NextVTableThunkIndex].first == I) {
586 const ThunkInfo &Thunk = VTableThunks[NextVTableThunkIndex].second;
587
588 maybeEmitThunkForVTable(GD, Thunk);
589 Init = CGM.GetAddrOfThunk(GD, Thunk);
590
591 NextVTableThunkIndex++;
592 } else {
593 llvm::Type *Ty = CGM.getTypes().GetFunctionTypeForVTable(GD);
594
595 Init = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
596 }
597
598 Init = llvm::ConstantExpr::getBitCast(Init, Int8PtrTy);
599 }
600 break;
601 }
602
603 case VTableComponent::CK_UnusedFunctionPointer:
604 Init = llvm::ConstantExpr::getNullValue(Int8PtrTy);
605 break;
606 };
607
608 Inits.push_back(Init);
609 }
610
611 llvm::ArrayType *ArrayType = llvm::ArrayType::get(Int8PtrTy, NumComponents);
612 return llvm::ConstantArray::get(ArrayType, Inits);
613 }
614
615 llvm::GlobalVariable *
GenerateConstructionVTable(const CXXRecordDecl * RD,const BaseSubobject & Base,bool BaseIsVirtual,llvm::GlobalVariable::LinkageTypes Linkage,VTableAddressPointsMapTy & AddressPoints)616 CodeGenVTables::GenerateConstructionVTable(const CXXRecordDecl *RD,
617 const BaseSubobject &Base,
618 bool BaseIsVirtual,
619 llvm::GlobalVariable::LinkageTypes Linkage,
620 VTableAddressPointsMapTy& AddressPoints) {
621 if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
622 DI->completeClassData(Base.getBase());
623
624 std::unique_ptr<VTableLayout> VTLayout(
625 getItaniumVTableContext().createConstructionVTableLayout(
626 Base.getBase(), Base.getBaseOffset(), BaseIsVirtual, RD));
627
628 // Add the address points.
629 AddressPoints = VTLayout->getAddressPoints();
630
631 // Get the mangled construction vtable name.
632 SmallString<256> OutName;
633 llvm::raw_svector_ostream Out(OutName);
634 cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext())
635 .mangleCXXCtorVTable(RD, Base.getBaseOffset().getQuantity(),
636 Base.getBase(), Out);
637 Out.flush();
638 StringRef Name = OutName.str();
639
640 llvm::ArrayType *ArrayType =
641 llvm::ArrayType::get(CGM.Int8PtrTy, VTLayout->getNumVTableComponents());
642
643 // Construction vtable symbols are not part of the Itanium ABI, so we cannot
644 // guarantee that they actually will be available externally. Instead, when
645 // emitting an available_externally VTT, we provide references to an internal
646 // linkage construction vtable. The ABI only requires complete-object vtables
647 // to be the same for all instances of a type, not construction vtables.
648 if (Linkage == llvm::GlobalVariable::AvailableExternallyLinkage)
649 Linkage = llvm::GlobalVariable::InternalLinkage;
650
651 // Create the variable that will hold the construction vtable.
652 llvm::GlobalVariable *VTable =
653 CGM.CreateOrReplaceCXXRuntimeVariable(Name, ArrayType, Linkage);
654 CGM.setGlobalVisibility(VTable, RD);
655
656 // V-tables are always unnamed_addr.
657 VTable->setUnnamedAddr(true);
658
659 llvm::Constant *RTTI = CGM.GetAddrOfRTTIDescriptor(
660 CGM.getContext().getTagDeclType(Base.getBase()));
661
662 // Create and set the initializer.
663 llvm::Constant *Init = CreateVTableInitializer(
664 Base.getBase(), VTLayout->vtable_component_begin(),
665 VTLayout->getNumVTableComponents(), VTLayout->vtable_thunk_begin(),
666 VTLayout->getNumVTableThunks(), RTTI);
667 VTable->setInitializer(Init);
668
669 return VTable;
670 }
671
672 /// Compute the required linkage of the v-table for the given class.
673 ///
674 /// Note that we only call this at the end of the translation unit.
675 llvm::GlobalVariable::LinkageTypes
getVTableLinkage(const CXXRecordDecl * RD)676 CodeGenModule::getVTableLinkage(const CXXRecordDecl *RD) {
677 if (!RD->isExternallyVisible())
678 return llvm::GlobalVariable::InternalLinkage;
679
680 // We're at the end of the translation unit, so the current key
681 // function is fully correct.
682 const CXXMethodDecl *keyFunction = Context.getCurrentKeyFunction(RD);
683 if (keyFunction && !RD->hasAttr<DLLImportAttr>()) {
684 // If this class has a key function, use that to determine the
685 // linkage of the vtable.
686 const FunctionDecl *def = nullptr;
687 if (keyFunction->hasBody(def))
688 keyFunction = cast<CXXMethodDecl>(def);
689
690 switch (keyFunction->getTemplateSpecializationKind()) {
691 case TSK_Undeclared:
692 case TSK_ExplicitSpecialization:
693 assert(def && "Should not have been asked to emit this");
694 if (keyFunction->isInlined())
695 return !Context.getLangOpts().AppleKext ?
696 llvm::GlobalVariable::LinkOnceODRLinkage :
697 llvm::Function::InternalLinkage;
698
699 return llvm::GlobalVariable::ExternalLinkage;
700
701 case TSK_ImplicitInstantiation:
702 return !Context.getLangOpts().AppleKext ?
703 llvm::GlobalVariable::LinkOnceODRLinkage :
704 llvm::Function::InternalLinkage;
705
706 case TSK_ExplicitInstantiationDefinition:
707 return !Context.getLangOpts().AppleKext ?
708 llvm::GlobalVariable::WeakODRLinkage :
709 llvm::Function::InternalLinkage;
710
711 case TSK_ExplicitInstantiationDeclaration:
712 llvm_unreachable("Should not have been asked to emit this");
713 }
714 }
715
716 // -fapple-kext mode does not support weak linkage, so we must use
717 // internal linkage.
718 if (Context.getLangOpts().AppleKext)
719 return llvm::Function::InternalLinkage;
720
721 llvm::GlobalVariable::LinkageTypes DiscardableODRLinkage =
722 llvm::GlobalValue::LinkOnceODRLinkage;
723 llvm::GlobalVariable::LinkageTypes NonDiscardableODRLinkage =
724 llvm::GlobalValue::WeakODRLinkage;
725 if (RD->hasAttr<DLLExportAttr>()) {
726 // Cannot discard exported vtables.
727 DiscardableODRLinkage = NonDiscardableODRLinkage;
728 } else if (RD->hasAttr<DLLImportAttr>()) {
729 // Imported vtables are available externally.
730 DiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
731 NonDiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
732 }
733
734 switch (RD->getTemplateSpecializationKind()) {
735 case TSK_Undeclared:
736 case TSK_ExplicitSpecialization:
737 case TSK_ImplicitInstantiation:
738 return DiscardableODRLinkage;
739
740 case TSK_ExplicitInstantiationDeclaration:
741 llvm_unreachable("Should not have been asked to emit this");
742
743 case TSK_ExplicitInstantiationDefinition:
744 return NonDiscardableODRLinkage;
745 }
746
747 llvm_unreachable("Invalid TemplateSpecializationKind!");
748 }
749
750 /// This is a callback from Sema to tell us that it believes that a
751 /// particular v-table is required to be emitted in this translation
752 /// unit.
753 ///
754 /// The reason we don't simply trust this callback is because Sema
755 /// will happily report that something is used even when it's used
756 /// only in code that we don't actually have to emit.
757 ///
758 /// \param isRequired - if true, the v-table is mandatory, e.g.
759 /// because the translation unit defines the key function
EmitVTable(CXXRecordDecl * theClass,bool isRequired)760 void CodeGenModule::EmitVTable(CXXRecordDecl *theClass, bool isRequired) {
761 if (!isRequired) return;
762
763 VTables.GenerateClassData(theClass);
764 }
765
766 void
GenerateClassData(const CXXRecordDecl * RD)767 CodeGenVTables::GenerateClassData(const CXXRecordDecl *RD) {
768 if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
769 DI->completeClassData(RD);
770
771 if (RD->getNumVBases())
772 CGM.getCXXABI().emitVirtualInheritanceTables(RD);
773
774 CGM.getCXXABI().emitVTableDefinitions(*this, RD);
775 }
776
777 /// At this point in the translation unit, does it appear that can we
778 /// rely on the vtable being defined elsewhere in the program?
779 ///
780 /// The response is really only definitive when called at the end of
781 /// the translation unit.
782 ///
783 /// The only semantic restriction here is that the object file should
784 /// not contain a v-table definition when that v-table is defined
785 /// strongly elsewhere. Otherwise, we'd just like to avoid emitting
786 /// v-tables when unnecessary.
isVTableExternal(const CXXRecordDecl * RD)787 bool CodeGenVTables::isVTableExternal(const CXXRecordDecl *RD) {
788 assert(RD->isDynamicClass() && "Non-dynamic classes have no VTable.");
789
790 // If we have an explicit instantiation declaration (and not a
791 // definition), the v-table is defined elsewhere.
792 TemplateSpecializationKind TSK = RD->getTemplateSpecializationKind();
793 if (TSK == TSK_ExplicitInstantiationDeclaration)
794 return true;
795
796 // Otherwise, if the class is an instantiated template, the
797 // v-table must be defined here.
798 if (TSK == TSK_ImplicitInstantiation ||
799 TSK == TSK_ExplicitInstantiationDefinition)
800 return false;
801
802 // Otherwise, if the class doesn't have a key function (possibly
803 // anymore), the v-table must be defined here.
804 const CXXMethodDecl *keyFunction = CGM.getContext().getCurrentKeyFunction(RD);
805 if (!keyFunction)
806 return false;
807
808 // Otherwise, if we don't have a definition of the key function, the
809 // v-table must be defined somewhere else.
810 return !keyFunction->hasBody();
811 }
812
813 /// Given that we're currently at the end of the translation unit, and
814 /// we've emitted a reference to the v-table for this class, should
815 /// we define that v-table?
shouldEmitVTableAtEndOfTranslationUnit(CodeGenModule & CGM,const CXXRecordDecl * RD)816 static bool shouldEmitVTableAtEndOfTranslationUnit(CodeGenModule &CGM,
817 const CXXRecordDecl *RD) {
818 return !CGM.getVTables().isVTableExternal(RD);
819 }
820
821 /// Given that at some point we emitted a reference to one or more
822 /// v-tables, and that we are now at the end of the translation unit,
823 /// decide whether we should emit them.
EmitDeferredVTables()824 void CodeGenModule::EmitDeferredVTables() {
825 #ifndef NDEBUG
826 // Remember the size of DeferredVTables, because we're going to assume
827 // that this entire operation doesn't modify it.
828 size_t savedSize = DeferredVTables.size();
829 #endif
830
831 typedef std::vector<const CXXRecordDecl *>::const_iterator const_iterator;
832 for (const_iterator i = DeferredVTables.begin(),
833 e = DeferredVTables.end(); i != e; ++i) {
834 const CXXRecordDecl *RD = *i;
835 if (shouldEmitVTableAtEndOfTranslationUnit(*this, RD))
836 VTables.GenerateClassData(RD);
837 }
838
839 assert(savedSize == DeferredVTables.size() &&
840 "deferred extra v-tables during v-table emission?");
841 DeferredVTables.clear();
842 }
843